The present invention relates to a device for bringing signals in the microwave range together.
Within the technical areas of satellite communication, target tracking radar and the like there are demands for an accurate alignment of high-directivity antenna systems. For perfect transmission quality when receiving signals from a satellite it is therefore important that the receiving antenna is directed towards the satellite at all times. It is also of great importance that an antenna of a target tracking radar is directed towards the target since this makes it possible to determine the position of the target with high accuracy.
An often used technique for determining the direction of an antenna system in relationship to the direction of the received signal is that the antenna system is equipped with four reception elements that are horizontally and vertically symmetrically placed around the main direction of the antenna system. By combining the received signals from the four antenna elements in a suitable way, signals can be formed which indicate the difference between the direction of the antenna system and the direction of the received signal. The signals can then be used for alignment of the antenna system. This technique is often referred to as the mono pulse system.
As an example it can be mentioned that if the signals received by the four antenna elements are referred to as A, B, C and D then difference signals of the form (A+B)-(C+D) and (A+D)-(B+C) can be suitably formed. It is also common to form the information carrying summation signal (A+B+C+D).
The frequencies used in the mentioned applications imply that wave-guides are used for signal transfer. When forming the difference and summation signals it is therefore suitable to use a component that usually goes under the name of "magic T". This component has the characteristics that when it is fed with two signals it forms both the sum of the signals, as well as the difference between them. The conventional magic T has both its inputs and one of the outputs placed in the same plane (but aimed in different directions) while the other output (the difference output) is perpendicular to the plane.
To be able to form the above-mentioned difference and summation signals in a comparator, one has to combine four magic T:s. Due to the geometrical form of the conventional magic T, the connection of the T:s becomes complicated with wave-guides, -knees, -bends etc. Due to this the devices become bulky and difficult to manufacture. The multitude of variations of the mechanical design is rather limited since there is also a constraint of equality regarding electrical "wave length" through the different branches of the comparator.
The conventional design of the magic T has therefore aquired imitations with different designs that are able to fit into more compact constructions. The American patent U.S. Pat. No. 3,918,011 is an example of such a construction. The patent describes a magic T where the two inputs are placed in parallel next to each other in one plane and where the two outputs are placed in the opposite direction and perpendicular to the input plane. This has been made possible by integrating a knee and impedance matching in the structure of the T.
The American patent U.S. Pat. No. 4,174,507 is another example of a magic T of a "low" design. The patent describes a conventional magic T where the perpendicular wave-guide from the difference output from the T is replaced with a wave-guide that is parallel to the inputs and the plane of the summation output. To match the wave-guide to the difference output, the wave-guide is placed so that a short circuited stub is formed, as well as a number of impedance matched devices being placed in the wave-guide and the T.
The currently known versions of the conventional T have, among other things, in common that they require relatively substantial devices for impedance matching. Nor are they directly adapted to be connected together in compact comparator devices.